JP2021177458A - Nonaqueous electrolyte power storage element and manufacturing method thereof - Google Patents

Abstract

To provide: a nonaqueous electrolyte power storage element using, as a positive electrode, lithium transition metal composite oxide with high manganese content, which has a high capacity density per volume of a positive electrode active material layer and in which the swelling of a container due to charge/discharge cycles is suppressed; and a manufacturing method thereof.SOLUTION: A nonaqueous electrolyte power storage element includes a positive electrode having a positive electrode active material layer, and a nonaqueous electrolyte. The positive electrode active material layer includes lithium transition metal composite oxide which has an α-NaFeO2 structure and in which the content of manganese with respect to transition metal exceeds 0.5 in molar ratio. The positive electrode active material layer has a porosity of 35% or less. The nonaqueous electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate having a fluorine atom and an oxygen atom.SELECTED DRAWING: Figure 1

Description

The present invention relates to a non-aqueous electrolyte power storage device and a method for manufacturing the same.

Non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte power storage elements other than non-aqueous electrolyte secondary batteries.

As a positive electrode active material for a non-aqueous electrolyte power storage element, a lithium transition metal composite oxide having _{an α-NaFeO type 2 crystal structure is known. Such a composite oxide, a so-called LiMeO type 2} active material in which the content of manganese to the transition metal (Me) is 0.5 or less in terms of molar ratio and the molar ratio of lithium to the transition metal is approximately 1. The non-aqueous electrolyte secondary battery used has been put into practical use.

On the other hand, in recent years, among lithium transition metal composite oxides having _{an α-NaFeO type 2} crystal structure, the content of manganese with respect to the transition metal, which is also considered to be a solid solution of _{Li 2} MnO ₃ and LiMeO _{2, is 0 in terms of molar ratio.} Lithium transition metal composite oxides having a molar ratio of lithium to a transition metal of more than .5 and more than 1 are known (see Patent Documents 1 and 2). Such a lithium transition metal composite oxide having a high manganese content and a high lithium content is attracting attention as a positive electrode active material having a large capacity per mass. By using a positive electrode active material having a large capacity, it can be expected that the energy density of the non-aqueous electrolyte power storage element will be further increased.

Japanese Unexamined Patent Publication No. 2012-104335 Japanese Unexamined Patent Publication No. 2013-191390

Since the particles of the lithium transition metal composite oxide having a high manganese content as described above generally have a low apparent density, the volume density per volume of the positive electrode active material layer when the positive electrode is produced is low. Therefore, when a positive electrode is produced using a lithium transition metal composite oxide having a high manganese content, it is desirable to increase the density of the positive electrode active material layer by pressing or the like. However, the non-aqueous electrolyte power storage element provided with the positive electrode active material layer containing the lithium transition metal composite oxide having a high manganese content and having a high density has an inconvenience that the container swelling due to the charge / discharge cycle becomes large.

An object of the present invention is a non-aqueous electrolyte power storage element using a lithium transition metal composite oxide having a high manganese content as a positive electrode, which has a high capacity density per volume of the positive electrode active material layer and is a container associated with a charge / discharge cycle. It is an object of the present invention to provide a non-aqueous electrolyte storage element in which swelling is suppressed, and a method for manufacturing such a non-aqueous electrolyte storage element.

The non-aqueous electrolyte power storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer and a non-aqueous electrolyte, and the positive electrode active material layer has an α-NaFeO ₂ structure and manganese for a transition metal. Contains a lithium transition metal composite oxide having a molar ratio of more than 0.5, the positive electrode active material layer has a porosity of 35% or less, and the non-aqueous electrolyte has a fluorine atom and an oxygen atom. It is a non-aqueous electrolyte storage element containing at least one of a phosphate and a borate having a fluorine atom and an oxygen atom.

The non-aqueous electrolyte power storage element according to another aspect of the present invention includes a positive electrode having a positive electrode active material layer and a non-aqueous electrolyte, and the positive electrode active material layer has an α-NaFeO ₂ structure and is a transition metal. The content of manganese to the electrode contains a lithium transition metal composite oxide having a molar ratio of more than 0.5, the apparent density of the positive electrode active material layer is 2.6 g / cm ³ or more, and the non-aqueous electrolyte is a fluorine atom. It is a non-aqueous electrolyte power storage element containing at least one of a phosphate having an oxygen atom and a borate having a fluorine atom and an oxygen atom.

A method for producing a non-aqueous electrolyte power storage element according to another aspect of the present invention includes preparing a positive electrode having a positive electrode active material layer and preparing a non-aqueous electrolyte, and the positive electrode active material layer is provided with the above-mentioned positive electrode active material layer. It has an α-NaFeO ₂ structure, contains a lithium transition metal composite oxide having a manganese content of more than 0.5 in molar ratio with respect to the transition metal, and the porosity of the positive electrode active material layer is 35% or less. A method for producing a non-aqueous electrolyte power storage element, wherein the non-aqueous electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate acid having a fluorine atom and an oxygen atom.

A method for producing a non-aqueous electrolyte power storage element according to another aspect of the present invention includes preparing a positive electrode having a positive electrode active material layer and preparing a non-aqueous electrolyte, and the positive electrode active material layer is provided with the above-mentioned positive electrode active material layer. It has an α-NaFeO ₂ structure, contains a lithium transition metal composite oxide having a manganese content of more than 0.5 in molar ratio with respect to the transition metal, and the apparent density of the positive electrode active material layer is 2.6 g / cm ³ or more. The non-aqueous electrolyte is a method for producing a non-aqueous electrolyte power storage element containing at least one of a phosphate having a fluorine atom and an oxygen atom and a borate acid having a fluorine atom and an oxygen atom.

According to one aspect of the present invention, it is a non-aqueous electrolyte power storage element using a lithium transition metal composite oxide having a high manganese content as a positive electrode, has a high capacity density per volume of the positive electrode active material layer, and has a charge / discharge cycle. It is possible to provide a non-aqueous electrolyte power storage element in which the swelling of the container is suppressed, and a method for manufacturing such a non-aqueous electrolyte power storage element.

FIG. 1 is an external perspective view showing a non-aqueous electrolyte power storage element according to an embodiment of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of non-aqueous electrolyte power storage elements according to an embodiment of the present invention.

First, an outline of the non-aqueous electrolyte power storage device disclosed by the present specification and a method for manufacturing the same will be described.

The non-aqueous electrolyte power storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer and a non-aqueous electrolyte, and the positive electrode active material layer has an α-NaFeO ₂ structure and manganese for a transition metal. Contains a lithium transition metal composite oxide having a molar ratio of more than 0.5, the positive electrode active material layer has a porosity of 35% or less, and the non-aqueous electrolyte has a fluorine atom and an oxygen atom. It is a non-aqueous electrolyte power storage element (A) containing at least one of a phosphate and a borate having a fluorine atom and an oxygen atom.

The non-aqueous electrolyte storage element (A) is a non-aqueous electrolyte storage element using a lithium transition metal composite oxide having a high manganese content for the positive electrode, and has a high capacity density per volume of the positive electrode active material layer and is filled. The swelling of the container due to the discharge cycle is suppressed.

The non-aqueous electrolyte power storage element according to another aspect of the present invention includes a positive electrode having a positive electrode active material layer and a non-aqueous electrolyte, and the positive electrode active material layer has an α-NaFeO ₂ structure and is a transition metal. The content of manganese to the electrode contains a lithium transition metal composite oxide having a molar ratio of more than 0.5, the apparent density of the positive electrode active material layer is 2.6 g / cm ³ or more, and the non-aqueous electrolyte is a fluorine atom. It is a non-aqueous electrolyte power storage element (B) containing at least one of a phosphate having an oxygen atom and a borate having a fluorine atom and an oxygen atom.

The non-aqueous electrolyte storage element (B) is also a non-aqueous electrolyte storage element using a lithium transition metal composite oxide having a high manganese content for the positive electrode, and has a high capacity density per volume of the positive electrode active material layer and is filled. The swelling of the container due to the discharge cycle is suppressed.

The reason why the above effect occurs is not clear, but the following can be presumed. Generally, when the positive electrode active material layer is densified by a press or the like, if the press pressure is large, the lithium transition metal composite oxide particles which are the positive electrode active material may be crushed. In such a case, an increase in the specific surface area due to the surface (new surface) of the particles newly generated by crushing tends to cause a side reaction with the non-aqueous electrolyte, so that the swelling due to gas generation tends to increase.

A _{lithium transition metal composite oxide having a high manganese content, which is considered to be a solid solution of Li 2} MnO ₃ and LiMeO ₂ , usually has a lithium content of more than 1 in terms of molar ratio to the transition metal, and thus is a lithium excess type. Also called active material. As a method for producing such a lithium transition metal composite oxide having a high manganese content, a hydroxide precursor is used as in the case _{of the LiMeO type 2 active material in which the molar ratio of lithium to the transition metal is approximately 1.} There is a method of passing through and a method of passing through a carbonate precursor.

When a lithium transition metal composite oxide having a high manganese content is prepared via a hydroxide precursor, the particles of the lithium transition metal composite oxide are _{bulkier than the particles of the LiMeO type 2} active material and appear to be bulky. The density will be low. The reason for this is that the crystal morphology of the primary particles of _{Ni (OH) 2} and Co (OH) ₂ is needle-shaped, whereas the crystal morphology of the primary particles of _{Mn (OH) 2 is hexagonal plate-shaped.} It is related and is derived from the high Mn ratio in the transition metal.

Further, it is said that a lithium transition metal composite oxide having a high manganese content can obtain a large capacity by utilizing the redox reaction of oxygen in addition to the redox reaction of the transition metal. However, the redox reaction of oxygen has a large reaction resistance. In such particles of a lithium transition metal composite oxide having a high manganese content, it is conceivable to increase the specific surface area as a method of reducing the reaction resistance. Therefore, by producing a lithium transition metal composite oxide having a high manganese content via a carbonate precursor, the primary particle size can be reduced and particles having a large specific surface area can be obtained. However, the secondary particles formed from such primary particles have many pores or voids between the primary particles. From this, even when a lithium transition metal composite oxide having a high manganese content is produced via a carbonate precursor, the particles of the lithium transition metal composite oxide are _{compared with the particles of the LiMeO type 2} active material. It is bulky and has a low apparent density.

From the above, the lithium transition metal composite oxide having a high manganese content usually has a lower apparent density than the _{LiMeO type 2 active material and the like.} Therefore, a positive electrode using a lithium transition metal composite oxide having a high manganese content as an active material is difficult to be filled with the positive electrode active material layer even when pressed under normal pressure, so that the positive electrode active material layer is made denser. If this is the case, it is necessary to press at a pressure higher than usual. In this pressing process, strong pressure is applied to the secondary particles of the active material, so that the voids and pores between the primary particles are crushed, and the secondary particles are easily crushed.

On the other hand, _{the particles of other active materials such as LiMeO type 2} active material are not bulky as compared with the active material of the lithium transition metal composite oxide having a high manganese content. By performing the pressing, a sufficiently high-density positive electrode active material layer can be obtained, so that the crushing of the active material secondary particles by the pressing process as described above is unlikely to occur.

That is, the non-aqueous electrolyte storage element (A) and the non-aqueous electrolyte storage element (B) have a high density of the positive electrode active material layer in the non-aqueous electrolyte storage element using a lithium transition metal composite oxide having a high manganese content as the positive electrode. It solves the peculiar problem that arises when trying to convert.

In the non-aqueous electrolyte power storage element (A), a phosphate having a fluorine atom and an oxygen atom contained in the non-aqueous electrolyte or a borate having a fluorine atom and an oxygen atom is contained on the surface of the active material particles. It is presumed that a good film of origin is formed. It is presumed that such a coating suppresses side reactions with non-aqueous electrolytes and suppresses container swelling due to gas generation. In the non-aqueous electrolyte power storage element (A), as a result of the high capacity density per volume of the positive electrode active material layer, the energy density per volume of the positive electrode active material layer can be high.

In the non-aqueous electrolyte storage element (B) as well, for the same reason as the above-mentioned non-aqueous electrolyte storage element (A), side reactions with the non-aqueous electrolyte are suppressed, and container swelling due to gas generation is suppressed. It is presumed. Further, also in the non-aqueous electrolyte power storage element (B), as a result of the high capacity density per volume of the positive electrode active material layer, the energy density per volume of the positive electrode active material layer can be high.

The porosity of the positive electrode active material layer is calculated by the following formula from the true density of the positive electrode active material layer calculated from the true density of each component constituting the positive electrode active material layer and the apparent density of the positive electrode active material layer. The value.
Porosity (%) = 100- (apparent density / true density) x 100

The apparent density of the positive electrode active material layer is a value obtained by dividing the mass of the positive electrode active material layer by the apparent volume of the positive electrode active material layer. The apparent volume refers to the volume including the void portion, and can be obtained as the product of the average thickness and the area of the positive electrode active material layer. The average thickness of the positive electrode active material layer shall be the average value of the thickness measured at any five locations.

The method for producing a non-aqueous electrolyte power storage element according to one aspect of the present invention includes preparing a positive electrode having a positive electrode active material layer and preparing a non-aqueous electrolyte, and the positive electrode active material layer is α-. It _{has a NaFeO 2} structure, contains a lithium transition metal composite oxide having a manganese content of more than 0.5 in molar ratio with respect to the transition metal, has a porosity of 35% or less of the positive electrode active material layer, and is non-aqueous. This is a method (A) for producing a non-aqueous electrolyte storage element in which the electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate having a fluorine atom and an oxygen atom.

According to the method (A) for manufacturing the non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element uses a lithium transition metal composite oxide having a high manganese content as the positive electrode, and has a capacity per volume of the positive electrode active material layer. It is possible to manufacture a non-aqueous electrolyte power storage element having a high density and suppressing container swelling due to a charge / discharge cycle.

A method for producing a non-aqueous electrolyte power storage element according to another aspect of the present invention includes preparing a positive electrode having a positive electrode active material layer and preparing a non-aqueous electrolyte, and the positive electrode active material layer is provided with the above-mentioned positive electrode active material layer. It has an α-NaFeO ₂ structure, contains a lithium transition metal composite oxide having a manganese content of more than 0.5 in molar ratio with respect to the transition metal, and the apparent density of the positive electrode active material layer is 2.6 g / cm ³ or more. In the method (B) for producing a non-aqueous electrolyte power storage element, wherein the non-aqueous electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate acid having a fluorine atom and an oxygen atom. be.

According to the method (B) for manufacturing the non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element uses a lithium transition metal composite oxide having a high manganese content as the positive electrode, and the volume density per volume of the positive electrode active material layer. It is possible to manufacture a non-aqueous electrolyte power storage element in which the swelling of the container due to the charge / discharge cycle is suppressed.

Hereinafter, a non-aqueous electrolyte power storage device according to an embodiment of the present invention and a method for manufacturing the same will be described in detail.

<Non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage device according to the embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode usually form electrode bodies that are alternately superposed by stacking or winding through a separator. The electrode body is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the container, a commonly used known metal container, resin container, or the like can be used. Hereinafter, as an example of the non-aqueous electrolyte power storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) will be described.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer arranged directly on the positive electrode base material or via an intermediate layer.

The positive electrode base material has conductivity. The A has a "conductive" means that the volume resistivity is measured according to JIS-H-0505 (1975 years) is not more than 10 ⁷ Ω · cm, "non-conductive", means that the volume resistivity is 10 ⁷ Ω · cm greater. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of the positive electrode base material include foils and vapor-deposited films, and foils are preferable from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085 and A3003 specified in JIS-H-4000 (2014).

The average thickness of the positive electrode base material is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. By setting the average thickness of the positive electrode base material to the above lower limit or more, the strength of the positive electrode base material can be increased. By setting the average thickness of the positive electrode base material to be equal to or less than the above upper limit, the energy density per volume of the secondary battery can be increased. The "average thickness" of the positive electrode base material and the negative electrode base material described later refers to a value obtained by dividing the punched mass when a base material having a predetermined area is punched by the true density of the base material and the punched area.

The intermediate layer is a layer arranged between the positive electrode base material and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited, and includes, for example, a resin binder and conductive particles. The intermediate layer contains, for example, conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode active material layer.

The positive electrode active material layer is a layer of a positive electrode mixture containing a positive electrode active material. The positive electrode active material layer (positive electrode mixture) may contain an optional component such as a conductive agent, a binder, a thickener, and a filler, if necessary, in addition to the positive electrode active material.

The positive electrode active material contains a lithium transition metal composite oxide. This lithium transition metal composite oxide has an α-NaFeO ₂ structure, and the content of manganese with respect to the transition metal exceeds 0.5 in terms of molar ratio. The lithium transition metal composite oxide may be a so-called lithium excess type active material in which the content of lithium with respect to the transition metal exceeds 1 in terms of molar ratio. By using such a positive electrode active material in the secondary battery, the capacity per mass becomes large.

The lithium transition metal composite oxide may be represented by the following formula 1.
Li _{1 + α} Me _1-α O ₂ ... 1
In Equation 1, 0 <α <1. The content of Li with respect to the transition metal (Me) is more than 1.0 in terms of molar ratio, preferably 1.1 or more or 1.2 or more, and sometimes 1.3 or more. The upper limit of the Li content with respect to the transition metal (Me) may be 1.5 or 1.45 in terms of molar ratio. This value is represented by (1 + α) / (1-α).

Me in the above formula 1 is a transition metal containing Mn. The content of Mn with respect to the transition metal (Me) is more than 0.5 in terms of molar ratio, and is preferably 0.55 or more or 0.6 or more. The upper limit of the Mn content with respect to the transition metal (Me) may be 0.7 in terms of molar ratio.

Me in the above formula 1 preferably contains Ni or Co in addition to Mn, and more preferably contains Ni. Me may contain other transition metal elements as long as the effects of the present invention are not impaired.

The content of Ni with respect to the transition metal (Me) is preferably 0.1 or more and less than 0.5, and more preferably 0.15 or more and 0.4 or less. By setting the Ni content within the above range, the energy density, capacity density, and the like are improved.

The content of Co with respect to the transition metal (Me) may be, for example, 0 or more and 0.3 or less.

The composition ratio of the lithium transition metal composite oxide in the present specification refers to the composition ratio when the lithium transition metal composite oxide is brought into a completely discharged state by the following method. First, the non-aqueous electrolyte power storage element is constantly charged with a current of 0.05 C until it reaches the end-of-charge voltage during normal use, and is brought into a fully charged state. After a 30-minute pause, a constant current discharge of 0.05 C to the lower limit voltage during normal use. It was disassembled, the positive electrode was taken out, a test battery with a metallic lithium electrode as the counter electrode was assembled, and the positive electrode potential was 2.0 V vs. at a current value of 10 mA per 1 g of the positive electrode mixture. A constant current discharge is performed until Li / Li ⁺ , and the positive electrode is adjusted to a completely discharged state. Re-disassemble and take out the positive electrode. The non-aqueous electrolyte adhering to the removed positive electrode is thoroughly washed with dimethyl carbonate, dried at room temperature for 24 hours, and then the lithium transition metal composite oxide of the positive electrode active material is collected. The collected lithium transition metal composite oxide is used for measurement. The work from disassembly of the non-aqueous electrolyte power storage element to measurement is performed in an argon atmosphere with a dew point of -60 ° C or lower. Here, the normal use is a case where the non-aqueous electrolyte storage element is used by adopting the charge / discharge conditions recommended or specified for the non-aqueous electrolyte storage element, and the non-aqueous electrolyte storage element of the non-aqueous electrolyte storage element. When a charger for this purpose is prepared, it means a case where the charger is applied to use the non-aqueous electrolyte power storage element.

The lithium transition metal composite oxide can be synthesized by various methods such as a solid phase method, a sol-gel method, a hydrothermal method, and a coprecipitation method. Among these, it is preferable to use a composite oxide synthesized by the coprecipitation method because the distribution of the transition metal is highly uniform. In the coprecipitation method, a precursor containing a transition metal such as Mn is prepared by precipitation (coprecipitation) in an aqueous solution, and a mixture of this precursor and a lithium compound is calcined to obtain a lithium transition metal composite oxide. It is a method of synthesizing. As the precursor obtained by the above coprecipitation, a hydroxide precursor or a carbonate precursor can be adopted.

The precursor may be a hydroxide precursor, but by adopting a carbonate precursor, a precursor having a high sphericity and a lithium transition metal composite oxide can be obtained. Therefore, by using this lithium transition metal composite oxide, it is possible to produce a positive electrode having a uniform and highly smooth positive electrode active material layer. The lithium transition metal composite oxide obtained from the carbonate precursor has a peak differential pore volume of 0.7 mm ³ / (g · nm) or more or 0.8 mm ³ / (g · nm) or more. There is a tendency.

In one embodiment of the present invention, the peak differential pore volume of the lithium transition metal composite oxide ^{is preferably 0.7 mm 3} / (g · nm) or more, more preferably 0.8 mm ³ / (g · nm) or more. .. When the peak differential pore volume of the lithium transition metal composite oxide is at least the above lower limit, the volume can be increased. On the other hand, a lithium transition metal composite oxide having a large peak differential pore volume is usually particularly liable to be crushed by a press or the like. Therefore, when a lithium transition metal composite oxide having a peak differential pore volume equal to or higher than the above lower limit is used, container swelling due to a charge / discharge cycle can be suppressed particularly effectively, and the present invention is adopted. The effect of suppressing the swelling of the container due to the above is remarkable. The upper limit of the peak differential pore volume of the lithium transition metal composite oxide may be, for example, 3 mm ³ / (g · nm) or 2.5 mm ³ / (g · nm).

The peak differential pore volume of the lithium transition metal composite oxide is a value obtained by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method. Specifically, the peak differential pore volume is measured by the following method. By placing 1.00 g of lithium transition metal composite oxide as a measurement sample in a sample tube for measurement and vacuum drying at 120 ° C. for 6 hours and then at 180 ° C. for 6 hours, the water content in the measurement sample is sufficiently removed. Remove. Next, the isotherms on the adsorption side and the desorption side are measured within a range of 0 to 1 relative pressure P / P0 (P0 = about 770 mmHg) by a nitrogen gas adsorption method using liquid nitrogen. Then, the cumulative pore volume curve is obtained by calculating by the BJH method using the isotherms on the desorption side. From this curve, the value of total pore volume (cm ³ / g) can be obtained. Next, by linearly differentiating the cumulative pore volume curve, the horizontal axis is the pore diameter (nm) and the vertical axis is the differential pore volume (mm ³ / (g · nm)). Obtaining a volume curve. In the present specification, the “peak differential pore volume” means the value on the vertical axis at the maximum point of the differential pore volume curve, and “the fineness in which the differential pore volume indicates the maximum value”. The “pore diameter” refers to the value on the horizontal axis at the maximum point of the differential pore volume curve.

The pore diameter at which the differential pore volume of the lithium transition metal composite oxide exhibits the maximum value is preferably in the range of 10 nm to 200 nm, and more preferably in the range of 20 nm to 100 nm. The total pore volume of the lithium transition metal composite oxide is preferably 0.03 cm ³ / g or more 0.2 cm ³ / g or less, more preferably 0.06 cm ³ / g or more 0.1 cm ³ / g .. When the pore diameter showing the maximum value of the differential pore volume of the lithium transition metal composite oxide or the total pore volume is within the above range, the capacity can be further increased, and when the present invention is adopted. The effect of suppressing container swelling appears more prominently.

The positive electrode active material may contain a positive electrode active material other than the above lithium transition metal composite oxide. The content of the lithium transition metal composite oxide in the positive electrode active material may be, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more. , 99% by mass or more is more preferable, and it may be substantially 100% by mass. By increasing the content ratio of the lithium transition metal composite oxide in the positive electrode active material, the volume density per volume of the positive electrode active material layer can be further increased.

As the positive electrode active material other than the above-mentioned lithium transition metal composite oxide, a known positive electrode active material usually used for a lithium ion secondary battery or the like can be appropriately selected. As the positive electrode active material, a material capable of occluding and releasing lithium ions is usually used. For example, the above-mentioned LiMeO _{type 2} active material, lithium transition metal oxide having a spinel type crystal structure, polyanion compound, chalcogen compound, sulfur and the like can be mentioned.

The average particle size of the positive electrode active material is preferably 0.1 μm or more and 20 μm or less, for example. By setting the average particle size of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved. Here, the "average particle size" is based on JIS-Z-8825 (2013), and is based on the particle size distribution measured by a laser diffraction / scattering method with respect to a diluted solution obtained by diluting the particles with a solvent. It means a value at which the volume-based integrated distribution calculated in accordance with Z-8819-2 (2001) is 50%.

A crusher, a classifier, or the like is used to obtain particles such as a positive electrode active material in a predetermined shape. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, and the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass or more and 99% by mass or less, more preferably 80% by mass or more and 98% by mass or less, and further preferably 90% by mass or more and 96% by mass or less. By setting the content of the positive electrode active material in the above range, the electric capacity of the secondary battery can be increased.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such a conductive agent include graphite; carbon black such as furnace black and acetylene black; metal; conductive ceramics and the like. Examples of the shape of the conductive agent include powder and fibrous. Among these, acetylene black is preferable from the viewpoint of electron conductivity and coatability.

The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. By setting the content of the conductive agent in the above range, the electric capacity of the secondary battery can be increased.

Examples of the binder include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, and the like. Elastomers such as styrene-butadiene rubber (SBR) and fluororubber; thermoplastic polymers and the like can be mentioned.

The binder content in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. By setting the binder content within the above range, the active material can be stably retained.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, this functional group may be inactivated by methylation or the like in advance.

The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, aluminosilicate and the like.

The positive electrode active material layer includes typical non-metal elements such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba and the like. Typical metal elements of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements are used as positive electrode active materials, conductive agents, binders, thickeners, fillers. It may be contained as a component other than.

The positive electrode active material layer may further contain a phosphorus oxo acid such as phosphonic acid or a component derived from the phosphorus oxo acid. In such a case, a film derived from phosphorus oxoacid is formed on the surface of the positive electrode active material layer to enhance the gas generation suppressing effect, and thus the container swelling due to the charge / discharge cycle is further suppressed.

In one embodiment of the present invention, the upper limit of porosity of the positive electrode active material layer is 35%, preferably 34%, 33% or 32%. When the porosity of the positive electrode active material layer is not more than the above upper limit, the volume density per volume of the positive electrode active material layer can be increased. On the other hand, the lower limit of the porosity of the positive electrode active material layer is preferably, for example, 25%, and may be more preferably 27% or 30%. When the porosity of the positive electrode active material layer is at least the above lower limit, it is possible to further suppress container swelling due to the charge / discharge cycle.

In another embodiment of the present invention, the lower limit of the apparent density of the positive electrode active material layer is ^{2.6g / cm 3, 2.7g / cm} 3 are preferred. When the apparent density of the positive electrode active material layer is at least the above lower limit, the volume density per volume of the positive electrode active material layer can be increased. The upper limit of the apparent density of the positive electrode active material layer, for example 3.2 g / cm ³ is preferable, 3.0 g / cm ³ is also more preferable. When the apparent density of the positive electrode active material layer is not more than the above upper limit, it is possible to further suppress the swelling of the container due to the charge / discharge cycle.

The porosity and apparent density of the positive electrode active material layer can be adjusted by adjusting the strength of the press pressure at the time of forming the positive electrode active material layer.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode active material layer arranged directly on the negative electrode base material or via an intermediate layer. The configuration of the intermediate layer of the negative electrode is not particularly limited, and the same configuration as that of the intermediate layer of the positive electrode can be used.

The negative electrode base material has conductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof are used. Among these, copper or a copper alloy is preferable. Examples of the negative electrode base material include foils and vapor-deposited films, and foils are preferable from the viewpoint of cost. Therefore, a copper foil or a copper alloy foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil, electrolytic copper foil and the like.

The average thickness of the negative electrode base material is preferably 3 μm or more and 30 μm or less, and more preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode base material to the above lower limit or more, the strength of the negative electrode base material can be increased. By setting the average thickness of the negative electrode base material to be equal to or less than the above upper limit, the energy density per volume of the secondary battery can be increased.

The negative electrode active material layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode active material layer (negative electrode mixture) may contain an optional component such as a conductive agent, a binder, a thickener, and a filler, if necessary, in addition to the negative electrode active material. As any component such as a conductive agent, a binder, a thickener, and a filler, the same one as that of the positive electrode active material layer can be used. The content of each of these optional components in the negative electrode active material layer can be in the range described as these contents in the positive electrode active material layer.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium ions is usually used. Examples of the negative electrode active material include metals Li; metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as Si oxides, Ti oxides and Sn oxides; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTIO _{2 and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite (graphite) and non-graphitable carbon (easy-to-graphite carbon or non-graphite-resistant carbon) can be mentioned. Be done. In the negative electrode active material layer, one of these materials may be used alone, or two or more of these materials may be mixed and used.

_{“Graphite” refers to a carbon material having an average lattice spacing (d 002} ) of (002) planes determined by X-ray diffraction before charging / discharging or in a discharged state of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material having stable physical properties can be obtained.

_{“Non-graphitic carbon” refers to a carbon material having an average lattice spacing (d 002} ) of (002) planes determined by X-ray diffraction before charging / discharging or in a discharged state of 0.34 nm or more and 0.42 nm or less. say. Examples of non-graphitizable carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-graphic carbon include a resin-derived material, a petroleum pitch or a petroleum pitch-derived material, a petroleum coke or a petroleum coke-derived material, a plant-derived material, an alcohol-derived material, and the like.

Here, the "discharge state" that defines graphite and non-graphitic carbon means that the open circuit voltage is 0 in a unipolar battery in which a negative electrode containing a carbon material as a negative electrode active material is used as a working electrode and metallic Li is used as a counter electrode. It means a state where the voltage is 7V or higher. Since the potential of the metal Li counter electrode in the open circuit state is substantially equal to the redox potential of Li, the open circuit voltage in the single pole battery is substantially equal to the potential of the negative electrode containing the carbon material with respect to the redox potential of Li. .. That is, the fact that the open circuit voltage of the single-pole battery is 0.7 V or more means that lithium ions that can be occluded and discharged are sufficiently released from the carbon material that is the negative electrode active material during charging and discharging. ..

The “non-graphitizable carbon” _{refers to a carbon material having d 002} of 0.36 nm or more and 0.42 nm or less.

The “graphitizable carbon” _{refers to a carbon material having d 002} of 0.34 nm or more and less than 0.36 nm.

The negative electrode active material is usually particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. By setting the average particle size of the negative electrode active material to be equal to or higher than the above lower limit, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electron conductivity of the active material layer is improved. A crusher, a classifier, or the like is used to obtain a powder having a predetermined particle size. The pulverization method and the powder grade method can be selected from, for example, the methods exemplified for the positive electrode.

The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer.

The negative electrode active material layer includes typical non-metal elements such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba and the like. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc. It may be contained as a component other than the viscous agent and the filler.

(Separator)
The separator can be appropriately selected from known separators. As the separator, for example, a separator composed of only a base material layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one surface or both surfaces of the base material layer can be used. Examples of the material of the base material layer of the separator include woven fabrics, non-woven fabrics, and porous resin films. Among these materials, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. As the base material layer of the separator, a material in which these resins are composited may be used.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500 ° C. in the atmosphere, and a mass loss of 5% when heated from room temperature to 800 ° C. in the atmosphere. The following are more preferable. Inorganic compounds can be mentioned as materials whose mass reduction is less than or equal to a predetermined value. As inorganic compounds, for example, oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, aluminosilicate; magnesium hydroxide, water. Hydroxides such as calcium oxide and aluminum hydroxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride and barium fluoride Covalently bonded crystals such as silicon and diamond; talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, mica and other mineral resource-derived substances or man-made products thereof. .. As the inorganic compound, a simple substance or a complex of these substances may be used alone, or two or more kinds thereof may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of the secondary battery.

The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a volume-based value, and means a value measured by a mercury porosity meter.

As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethylmethacrylate, polyvinylacetate, polyvinylpyrrolidone, polyvinylidene fluoride and the like. The use of polymer gel has the effect of suppressing liquid leakage. As the separator, a polymer gel may be used in combination with the above-mentioned porous resin film or non-woven fabric.

(Non-aqueous electrolyte)
The non-aqueous electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate salt having a fluorine atom and an oxygen atom. The non-aqueous electrolyte may be a non-aqueous electrolyte solution. When the non-aqueous electrolyte is a non-aqueous electrolyte solution, it further contains a non-aqueous solvent and an electrolyte salt in addition to at least one of the above phosphate and borate.

A phosphate having a fluorine atom and an oxygen atom usually contains a fluorine atom and an oxygen atom in the anions constituting the phosphate. The phosphate may be a lithium salt, a sodium salt, a potassium salt, a magnesium salt, an onium salt or the like, but among these, the lithium salt is preferable.

Examples of the phosphate having a fluorine atom and an oxygen atom include lithium difluorophosphate, lithium monofluorophosphate, lithium difluorodioxalatrine, lithium tetrafluorooxalate, and the like, and lithium difluorophosphate is preferable. ..

A borate having a fluorine atom and an oxygen atom usually contains a fluorine atom and an oxygen atom in the anions constituting the borate. The borate may be a lithium salt, a sodium salt, a potassium salt, a magnesium salt, an onium salt or the like, but among these, the lithium salt is preferable.

As the borate having a fluorine atom and an oxygen atom, lithium difluorooxalate borate is preferable.

The content of at least one of the phosphate having a fluorine atom and an oxygen atom and the borate salt having a fluorine atom and an oxygen atom in the non-aqueous electrolyte is preferably 0.01% by mass or more and 3% by mass or less. , 0.1% by mass or more and 2% by mass or less is more preferable, and 0.3% by mass or more and 1% by mass or less is more preferable. By setting the content to the above lower limit or more, a sufficient film can be formed, and container swelling due to gas generation can be further suppressed. On the other hand, by setting the content to the above upper limit or less, the charge / discharge performance of the non-aqueous electrolyte power storage element can be improved.

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, carboxylic acid ester, phosphoric acid ester, sulfonic acid ester, ether, amide, nitrile and the like.

As the non-aqueous solvent, a solvent in which a part of hydrogen atoms is replaced with halogen may be used. Fluorine is preferable as the halogen. By using a fluorinated solvent in which a part of hydrogen atoms is replaced with fluorine, that is, a solvent having a fluorinated atom such as a fluorinated cyclic carbonate or a fluorinated chain carbonate, it is sufficient even under usage conditions where the positive electrode potential reaches a high potential. Can be used for. The content of the fluorinated solvent in the non-aqueous solvent is preferably 50% by volume or more, more preferably 70% by volume or more, 90% by volume or more, or 100% by volume.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate. (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like can be mentioned. Among these, fluorinated cyclic carbonate is preferable, and FEC is more preferable.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate (TFEMC), and bis (trifluoroethyl) carbonate. Among these, fluorinated chain carbonate is preferable, and TFEMC is more preferable.

As the non-aqueous solvent, it is preferable to use cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. By using the cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte solution can be improved. By using the chain carbonate, the viscosity of the non-aqueous electrolytic solution can be kept low. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

The electrolyte salt can be appropriately selected from known electrolyte salts. It is assumed that this electrolyte salt does not contain a phosphate having a fluorine atom and an oxygen atom and a borate salt having a fluorine atom and an oxygen atom. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like. Of these, lithium salts are preferred.

Lithium salts include inorganic lithium salts such _{as LiPF 6} , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) _{2 , LiSO 3} CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ). ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) _3, etc. Lithium salts having halogenated hydrocarbon groups, etc. Can be mentioned. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The content of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol / dm ³ or more 2.5 mol / dm ³ or less, 0.3 mol / dm ³ or more 2.0 mol / dm ^3, more preferably less, 0.5 mol / dm ³ or more 1.7 mol / dm ³ and more preferably less, 0.7 mol / dm ³ or more 1.5 mol / dm ³ or less is particularly preferred. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

The non-aqueous electrolyte may further contain additives. Examples of such additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrides of terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran; 2-fluoro. Partial halides of the above aromatic compounds such as biphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoro Halogenated anisole compounds such as anisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, Ethylene Sulfate, Sulforane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyl Oxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisol, diphenyldisulfide, dipyridinium disulfide, 1,3-propensulton, 1,3-propanesulton, 1,4-butanesulton, 1,4 -Butensulton, perfluorooctane, tritrimethylsilyl borate, tritrimethylsilyl phosphate, tetrakistrimethylsilyl titanate and the like can be mentioned. These additives may be used alone or in combination of two or more.

The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, and 0.2. It is more preferably mass% or more and 5 mass% or less, and particularly preferably 0.3 mass% or more and 3 mass% or less. By setting the content of the additive in the above range, it is possible to improve the capacity maintenance performance or charge / discharge cycle performance after high-temperature storage, and further improve the safety.

As the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

The solid electrolyte can be selected from any material having ionic conductivity such as lithium, sodium and calcium and being solid at room temperature (for example, 15 ° C. to 25 ° C.). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes and the like.

Examples of the sulfide solid electrolyte include Li _{2 SP 2} S ₅ , Li I-Li _{2 SP 2} S ₅ , Li ₁₀ Ge-P ₂ S _{12, and the} like.

<Manufacturing method of non-aqueous electrolyte power storage element>
The method for manufacturing a non-aqueous electrolyte power storage element according to an embodiment of the present invention is to prepare a positive electrode having a positive electrode active material layer (positive electrode preparation step) and to prepare a non-aqueous electrolyte (non-aqueous electrolyte preparation step). And.

The positive electrode preparation step may be a step of producing a positive electrode. The positive electrode can be produced by applying the positive electrode mixture paste directly to the positive electrode base material or via an intermediate layer, and pressing the coated layer (positive electrode active material layer) after drying. The positive electrode mixture paste contains each component constituting the positive electrode active material layer (positive electrode mixture) such as the positive electrode active material, and a dispersion medium. The positive electrode active material includes the above-mentioned lithium transition metal composite oxide.

In one embodiment of the manufacturing method, the porosity of the positive electrode active material layer is adjusted to 35% or less depending on the strength of the press pressure or the like. As a result, _{a positive electrode active material layer having an α-NaFeO 2} structure, containing a lithium transition metal composite oxide having a manganese content of more than 0.5 in molar ratio with respect to the transition metal, and having a porosity of 35% or less is formed. Will be done.

Further, in another embodiment of the manufacturing method, the apparent density of the positive electrode active material layer ^{is adjusted to 2.6 g / cm 3} or more depending on the strength of the press pressure or the like. As a result, the positive electrode activity _{has an α-NaFeO 2} structure, contains a lithium transition metal composite oxide having a manganese content of more than 0.5 in molar ratio with respect to the transition metal, and an apparent density of 2.6 g / cm ³ or more. A material layer is formed.

In the production method, it is preferable to use a lithium transition metal composite oxide having a peak differential pore volume of 0.7 mm ³ / (g · nm) or more and further 0.8 mm ^{3 / (g · nm) or more.} ..

The non-aqueous electrolyte preparation step is a step of preparing a non-aqueous electrolyte containing at least one of a phosphate having a fluorine atom and an oxygen atom and a borate salt having a fluorine atom and an oxygen atom. The non-aqueous electrolyte preparation step may be a step of preparing the non-aqueous electrolyte. The preparation of the non-aqueous electrolyte is described, for example, in a non-aqueous solvent, an electrolyte salt, at least one of a phosphate having a fluorine atom and an oxygen atom and a borate having a fluorine atom and an oxygen atom, and optionally an additive. Can be done by mixing.

The method for manufacturing the non-aqueous electrolyte power storage element includes preparing a positive electrode, preparing a non-aqueous electrolyte, preparing a negative electrode, and laminating or winding the positive electrode and the negative electrode via a separator. By doing so, the electrode body may be formed, the electrode body may be housed in a container, and the non-aqueous electrolyte may be injected into the container. After the injection, the non-aqueous electrolyte power storage element can be obtained by sealing the injection port. Further, the non-aqueous electrolyte power storage element may be obtained by performing initial charge / discharge on the uncharged / discharged power storage element that has been assembled and the injection port is sealed.

<Other Embodiments>
The power storage element of the present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

Further, in the above-described embodiment, the non-aqueous electrolyte storage element is mainly a non-aqueous electrolyte secondary battery, but other non-aqueous electrolyte storage elements may be used. Examples of other non-aqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 1 shows a schematic view of a rectangular non-aqueous electrolyte storage element 1 (non-aqueous electrolyte secondary battery) which is an embodiment of the non-aqueous electrolyte storage element according to the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte power storage element 1 shown in FIG. 1, the electrode body 2 is housed in the container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

The configuration of the non-aqueous electrolyte power storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above-mentioned non-aqueous electrolyte power storage elements. An embodiment of the power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte power storage elements 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1]
As a positive electrode active material, it has an α-NaFeO ₂ structure and Li _{1 + α} (Ni _0.33 Mn _0.67 ) _1-α O ₂ ((1 + α) / (1-α) = 1.33, α = 0. The lithium transition metal composite oxide represented by .14) was prepared. When the pore distribution of the lithium transition metal composite oxide was measured by the above method, the pore diameter showing the maximum value of the differential pore volume was in the range of 40 nm to 80 nm, and the peak differential pore volume was 0.98 mm. ^{It was 3} / (g · nm). The total pore volume was 0.075 cm ³ / g. By mass ratio, the positive electrode active material: acetylene black (AB): polyvinylidene fluoride (PVDF) = 94.75: 3.0: 2.25 (solid matter equivalent) is contained, and N-methylpyrrolidone (NMP) is contained. A mixture used as a dispersion medium was prepared. To this mixture, as an additive, 0.5% by mass of phosphorous acid (H ₃ PO ₃ ) with respect to the mass of the positive electrode active material was added to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to an aluminum foil as a positive electrode base material, dried and pressed to obtain a positive electrode A. The porosity and apparent density of the positive electrode active material layer of the obtained positive electrode A were calculated by the above method. The porosity was 32% and the apparent density was 2.77 g / cm ³ .
A metallic lithium negative electrode was produced as the negative electrode.
A microporous polyolefin membrane was prepared as a separator.
As a non-aqueous electrolyte, FEC and TFEMC were dissolved in a non-aqueous solvent mixed at a volume ratio of 30:70 so that lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt had a content of 1.0 mol / dm ^3. The prepared solution was prepared. Further, about 0.5% by mass of lithium difluorophosphate (LiDFP) was mixed with this solution to prepare a non-aqueous electrolyte. This non-aqueous electrolyte was prepared as a saturated solution of LiDFP.
An electrode body was produced by laminating the positive electrode A and the negative electrode via the separator. This electrode body was housed in a container, the non-aqueous electrolyte was injected into the container, and then the electrode body was sealed to obtain the non-aqueous electrolyte power storage element of Example 1.

[Example 2, Comparative Examples 1 and 2]
The same procedure as in Example 1 was carried out, except that the compound shown in Table 1 was mixed with the non-aqueous electrolyte in an amount of 0.5% by mass instead of lithium difluorophosphate (LiDFP), or the compound was not mixed. Each non-aqueous electrolyte power storage element of Example 2 and Comparative Examples 1 and 2 was obtained. In the table, LiDFP indicates "lithium difluorophosphate", LiDFOB indicates "lithium difluorooxalatoborate", and TMSP indicates "tris (trimethylsilyl) phosphate". In addition, "-" in the table indicates that the corresponding compound is not mixed.

[Reference example 1]
A positive electrode B was obtained in the same manner as in Example 1 except that the pressing pressure was weakened as compared with the case of producing the positive electrode A of Example 1 and the pressing was performed. The porosity and apparent density of the positive electrode active material layer of the obtained positive electrode B were calculated by the above method. The porosity was 40% and the apparent density was 2.45 g / cm ³ . The non-aqueous electrolyte power storage element of Reference Example 1 was obtained in the same manner as in Example 1 except that the positive electrode B was used as the positive electrode.

[Reference Examples 2 to 4]
Reference is made in the same manner as in Reference Example 1 except that 0.5% by mass of the compound shown in Table 1 was mixed with the non-aqueous electrolyte in place of lithium difluorophosphate (LiDFP), or the compound was not mixed. Each non-aqueous electrolyte power storage element of Examples 2 to 4 was obtained.

(Initial charge / discharge)
Each of the obtained non-aqueous electrolyte power storage elements was initially charged and discharged for two cycles at 25 ° C. under the following conditions. Charging was performed by constant current constant voltage (CCCV) charging with a charging current of 0.1 C and a charging voltage of 4.7 V, and the charging termination condition was until the charging current reached 0.05 C. The discharge was a constant current (CC) discharge with a discharge current of 0.1 C and a discharge end voltage of 2.0 V. A 10-minute rest period was provided after charging and discharging. Based on the amount of electricity discharged in the second cycle, the volume density (mAh / cm ³ ) per volume of the positive electrode active material layer was determined.

(Charge / discharge cycle test)
Next, each non-aqueous electrolyte power storage element after the initial charge / discharge was subjected to a 50-cycle charge / discharge cycle test at 25 ° C. under the following conditions.
Charging was performed by constant current constant voltage (CCCV) charging with a charging current of 0.2 C and a charging voltage of 4.7 V, and the charging termination condition was until the charging current reached 0.05 C. The discharge was a constant current (CC) discharge with a discharge current of 0.1 C and a discharge end voltage of 2.0 V. A 10-minute rest period was provided after charging and discharging.
Before and after the charge / discharge cycle test, the volume of each non-aqueous electrolyte power storage element was measured, and the volume increase rate (%) after the charge / discharge cycle test was determined.

^{Table 1 shows the volume density (mAh / cm 3} ) and the volume increase rate (%) per volume of the positive electrode active material layer of each non-aqueous electrolyte storage element.

The following can be confirmed from Table 1. Comparing Comparative Example 2 and Reference Example 4, when the porosity of the positive electrode active material layer is lowered or the apparent density is increased, the volume density per volume of the positive electrode active material layer is increased, but the volume after the charge / discharge cycle is increased. The rate of increase increases. From the comparison between Comparative Example 2 and Reference Example 4, the increase in volume increase rate after the charge / discharge cycle, that is, the increase in container swelling, becomes remarkable when the positive electrode active material layer is densified. It can be said that there is.
In contrast to Comparative Example 2 above, Examples 1 and 2 containing LiDFP, which is a phosphate having a fluorine atom and an oxygen atom, or LiDFOB, which is a borate salt having a fluorine atom and an oxygen atom, in a non-aqueous electrolyte It can be seen that the volume increase rate is reduced while maintaining a high capacitance density. However, Comparative Example 1 in which TMSP was contained in the non-aqueous electrolyte did not show the effect of reducing the volume increase rate.
On the other hand, when the positive electrode active material layer was not densified as in Reference Examples 1 to 3, the effect of reducing the volume increase rate did not appear even if each compound was mixed with the non-aqueous electrolyte. It is presumed that this is because the effect of gas generation when each compound is decomposed is greater than the effect of suppressing gas generation by the film formed by each compound.
As described above, the effect of suppressing the volume increase rate after the charge / discharge cycle is obtained when a non-aqueous electrolyte containing a specific compound is applied to the non-aqueous electrolyte power storage element provided with the densified positive electrode active material layer. It can be confirmed that it is a peculiar effect that occurs in.

The present invention can be applied to electronic devices such as personal computers and communication terminals, non-aqueous electrolyte power storage elements used as power sources for automobiles, and the like.

1 Non-aqueous electrolyte power storage element 2 Electrode body 3 Container 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Power storage unit 30 Power storage device

Claims (4)

A positive electrode having a positive electrode active material layer and a non-aqueous electrolyte are provided.
The positive electrode active material layer _{contains a lithium transition metal composite oxide having an α-NaFeO 2} structure and having a manganese content of more than 0.5 in terms of molar ratio with respect to the transition metal.
The porosity of the positive electrode active material layer is 35% or less.
A non-aqueous electrolyte storage element in which the non-aqueous electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate salt having a fluorine atom and an oxygen atom. A positive electrode having a positive electrode active material layer and a non-aqueous electrolyte are provided.
The positive electrode active material layer _{contains a lithium transition metal composite oxide having an α-NaFeO 2} structure and having a manganese content of more than 0.5 in terms of molar ratio with respect to the transition metal.
The apparent density of the positive electrode active material layer is 2.6 g / cm ³ or more.
A non-aqueous electrolyte storage element in which the non-aqueous electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate salt having a fluorine atom and an oxygen atom. It comprises preparing a positive electrode having a positive electrode active material layer and preparing a non-aqueous electrolyte.
The positive electrode active material layer _{contains a lithium transition metal composite oxide having an α-NaFeO 2} structure and having a manganese content of more than 0.5 in terms of molar ratio with respect to the transition metal.
The porosity of the positive electrode active material layer is 35% or less.
A method for producing a non-aqueous electrolyte power storage element, wherein the non-aqueous electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate salt having a fluorine atom and an oxygen atom. It comprises preparing a positive electrode having a positive electrode active material layer and preparing a non-aqueous electrolyte.
The positive electrode active material layer _{contains a lithium transition metal composite oxide having an α-NaFeO 2} structure and having a manganese content of more than 0.5 in terms of molar ratio with respect to the transition metal.
The apparent density of the positive electrode active material layer is 2.6 g / cm ³ or more.
A method for producing a non-aqueous electrolyte power storage element, wherein the non-aqueous electrolyte contains at least one of a phosphate having a fluorine atom and an oxygen atom and a borate salt having a fluorine atom and an oxygen atom.

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